Aircraft fuel load equalizing system



Sept. 23, 1958 J.- L. UNDERWOOD, JR

AIRCRAFT FUEL. LOAD EQUALIZING SYSTEM n 1 4o 37 3739 l i'b'ub I35 L"uuu: L (L 1 AILERON CONTROL LINKAGE 82o TRIM TAB CONTROL LINKAGE 66oINVENTORL JOHN L. UNDERWOOD JR.

Unitd States The invention described herein may be manufactured and usedby or for the Government of the United States of America forgovernmental purposes without the payment of any royalties thereon ortherefor.

The present invention relates to an aircraft fuel load equalizing systemand more particularly to such a system employing an interconnectionbetween the trim tab members of an aircraft and pump means whichcontrols the flow of fuel between the fuel tanks of the aircraft. Thepresent application is a continuation-in-part of application Serial No.464,660, filed October 25, 1954, now Patent No. 2,755,046, issued July17, 1956.

The invention system. is particularly adapted for use in aircraftutilizing auxiliary wing tip fuel tanks or fuel tanks disposed withinthe wing adjacent the wing tip. In such aircraft, malfunctionsfrequently occur in the fuel feed system causing a tank on one side ofthe longitudinal axis of the aircraft to empty faster than a tank on theother side thereof. The resulting difference in weight of the fuel tankscauses the aircraft to become unbalanced about the longitudinal axisthereof, creating a hazardous condition which is particularly dangerousat slow speeds as for instance when landing the aircraft.

As a fuel load unbalance occurs during flight, the pilot of the aircraftsubconsciously adjusts the aileron trim tabs to relieve stick pressureresulting from the unequal loading. The apparent wing heaviness is notnoticeable to the pilot until the trim tabs are at the limit of theirmovement at which time a dangerous unbalance already exists. In order tosafely land the aircraft or even approach landing speeds when one wingtip tank is subst-antially heavier than the other, the pilot must eitherjettison one or both tanks, or jettison the fuel from the tanlcs. Eitherof these alternatives 'is expensive and undesirable.

Since the aileron trim tabs are adjusted to compensate for wingheaviness, the deflection of the aileron trim tabs is a measure of thewing heaviness as caused by an unequal fuel distribution. As disclosedin the parent application an interconnection is provided between theaileron trim tabs and a means which controls the flow of fuel from thefuel tanks whereby predetermined movement of the trim tabs automaticallycompensates for unequal flow of fuel from the tanks. In the parentapplication, a fuel control means such as a valve is provided in theconduits connecting the fuel tanks to the main fuel tank of theaircraft, a separate fuel control means being provided for each of thefuel tanks.

The structure as disclosed in the parent application has certaininherent limitations since the balancing action is dependent upon theflow of fuel from only one of the fuel tanks due to the fact that whenthe system is in the process of balancing the aircraft, one fuel tank isemptying while the other one is not emptying. In addition, if the meansfor transferring fuel from either of the fuel tanks of the system asshown in the parent application should become inoperative, the fuel insuch atent l 2,853,259 Patented Sept. 23, 1958 tank may not betransferred to the engines of the aircraft.

The improved system as disclosed in the present application provides anarrangement wherein an auxiliary conduit provides communication betweenthe oppositely disposed tanks of the aircraft and a reversible pumpconnected in the auxiliary conduit whereby fuel may be transferredbetween the oppositely disposed tanks. In such an arrangement, a fasterbalancing action may be obtained due to the fact that while the heaviertank is emptying the lighter tank is being filled thereby providing adifferential action which serves to balance the aircraft approximatelytwice as fast as is possible with the structure disclosed in the parentapplication. Furthermore, all the fuel carried in each of the fuel tanksmay be transferred to the main fuel tank or the engines of the aircrafteven though the means for transferring fuel from one of the tanks shouldbecome inoperative.

An object of the present invention is the provision of a new and novelaircraft fuel load equalizing system which senses unequal fuel loads inwing tip or outer wing fuel tanks.

Yet another object is the provision of a fuel load equalizing systemwhich provides the optimum balancing speed and wherein all the fuelcontained in the opposite fuel tanks thereof may be successfullytransferred to the engines of the aircraft even though the conventionaltransferring means for either of the tanks should become inoperative.

A further object of the invention is the provision of a fuel loadequalizing system which is simple and inexpensive in construction, yetsensitive and reliable in operation.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawing which shows a diagrammatic viewof a preferred embodiment of the invention.

Referring now to the drawing, oppositely disposed fuel tanks 10 and 11which are disposed either within the wings of the aircraft or at thewing tips thereof are respectively connected by means of conduits 12 and13 to a common conduit 14 which may be connected either to the main fueltank or the engines of the aircraft. Suitable conventional means (notshown) such as air pressure is connected to each of fuel tanks 10 and 11for forcing the fuel from the fuel tanks into conduits 12 and 13.

An auxiliary conduit 20 is connected to each of fuel tanks 1% and 11 andprovides communication therebetween. A fuel pump 21 is connected inconduit 20 and is adapted to be driven in opposite directions by a reversible electric motor 22 which is driven in opposite directionsdependent on the directions of electric current flow therethrough. Thecapacity of pump 21 and the operational characteristics of motor 22 maybe selected to provide optimum balancing speed to the system inaccordance with well-known design criteria.

A suitable source of electrical energy such as a battery 25 has thenegative pole thereof connected to ground and the positive pole thereofconnected to a terminal 26 through a switch 27. Switch 27 is located inthe cockpit of the aircraft such that the pilot may selectivelydeactivate the circuit when he desires. Two similar double pole,solenoid operated switches indicated generally by reference numerals 3dand 31 are normally biased to open position and are provided with coils32 and 33 respectively. Terminals 35 and 36 of switches 30 and 31respectively ice are connected to one terminal 37 of electric motor 22,and terminals 38 and 39 of the two switches are connected to theopposite terminal 40 of the electric motor. The

terminals 45 and 46 of switches 30 and 31 respectively are connected toground and it should be noted that the coils of each of the switches arealso connected to ground in a similar manner. The terminals 47 and 48 ofswitches 39 'and 31 respectively are connected to the positive pole ofthe battery and the positive pole of the battery is alsoconnectedbymeans of lead 50 to the pivotal axis 51 of a switch arm 52 therebyproviding'electrical'energy to the switch arm at all times.

Switch arm 52 is normally biased into neutral position as shown in thedrawings by means of oppositely disposed springs '54 and 55 andisprovided with a plurality of oppositely disposed contacts 56 and 57at-one end thereof. The opposite end of switch arm 52 is provided with acam member 58 which is adapted to engage a cooperating cam member andthereby actuate the switch arm in opposite directions as more fullyhereinafter described.

Contact 56 is adapted to engage a contact 60 which is connected by meansof lead 61 to coil 32 of switch and contact 57 is adapted to engage acontact 62 which is connected by means of lead 63 to coil 33 of switch31.

Reference character 65 indicates a portion of the left wing of theaircraft which rotatably journals a cam memher 66 suitably connected tothe control linkage 66a extending to the cockpit of the aircraft foroperating the aileron trim tabs thereof. Cam member 66 is provided witha cam surface 67 adapted to engage cam member 58 of switch arm 52 forpivoting the switch arm in opposite directions. An aileron 70 ispivotally supported adjacent the trailing edge of wing 65 and a trim tab71 is pivotally supported adjacent the trailing edge of aileron 70. Trimtab 71 is provided with a suitable quadrant 72 which is connected byconventional means such as a cable or the like indicated by dotted lines73 to a similar quadrant 74 connected to cam member 66 and theassociated trim tab control linkage. It is accordingly apparentthat'byoperation of the trim tab control linkage, cam member 66 isrotated thereby pivoting trim tab 71 about its pivotal axis 75, and thecam surface 67 of cam member 66 will engage cam member 58 of switch arm52 to suitably energize the above described electrical control circuit.Aileron 70 is provided with a suitable quadrant 80 which is connected byconventional means such as a cable or the like indicated by dotted lines81 to a similar quadrant 82 suitably journaled in wing 65, quadrant 82being connected to the conventional control linkage 82a extending to thecockpit of the aircraft whereby the pilot can selectively actuateaileron 70 independently of trim tab 71.

Operation of the invention system is as follows:

Assuming that trim tab 71 is mounted upon the aileron 70 of the leftwing 65 of the aircraft and that the left wing tank 10 is heavier thanthe right wing tank 11, the pilot will subconsciously actuate thecontrol linkage 6611 'such that cam member 66 is rotated in a clockwisedirection as seen in the drawing causing trim tab 71 to pivot in anupward direction. Such deflection of the trim tab will cause aileron 70to be lowered thereby increasing the lift on wing 65 and tending toraise the left wing and compensate for the left wing heaviness.

As cam member 66 rotates clockwise, it engages cam member 58 whichpivots the opposite portion of switch arm 52 in an upward direction suchthat contact 56 engages contact 60. The positive pole of the battery isthen connected through lead 50, switch arm 52, and lead 61 to the coil32 of switch 30 and subsequently to ground whereby coil 32 is energizedclosing switch 30, connecting contacts and 47 and contacts 38 and 45 toone another. A circuit is thereby closed through electric motor 22, andthe current flow therethrough is such that the pump rotates in thedirection to pump fuel from tank 10 into tank 11. It is evident that asthe fuel flows from the heavier left tank 10 into the lighter right tank11, the weight of tank 10 decreases and the weight of tank 11 increaseswhereby such diiferential action rapidly balances the weights of thetanks and relieves the unbalanced condition of the load.

When tank 11 ha substantially the same weight as tank 10, the heavinessof the left wing will no longer exist and the pilot will subconsciouslyreadjust trim tab 71 to its original position. Switch arm 52 is thenbiased to its neutral position by springs 54 and 55, opening the circuitthrough coil 32 of switch 30 thereby allowing switch 30 to be biased toopen position interrupting the current flow through electric motor 22and stopping the operation of pump 21. Should the right wing tank 11become heavier than the left wing tank 18, cam member 66 will be rotatedin a counterclockwise direction, engaging switch arm 52 in such a manneras to close the circuit through switch 31 thereby closing the switch andenergizing electric motor 22 in such a direction that fuel is pumpedfrom tank 11 into tank It In this manner, fuel is pumped from the slowerfeeding tank into the faster feeding tank at all times during operationof the aircraft, maintaining a balanced condition thereof during flight.

It is apparent that any suitable interconnection between the controllinkage 66a for the trim tabs and switch arm 52 may be employed, and cammembers 66 and 58 y are suitably dimensioned such that contacts 56 and57 engage contacts 60 and '62 respectively upon movement of the trim tabcontrol linkage to compensate for a wing heaviness on the order-ofpounds.

Cam member is preferably adjusta'bly secured to the trim tab controllinkage 66a such that the relative position of cam member 66 and thecontrol link-age may be slidably adjusted. With such an arrangement, itis possible for the pilot to trim the aircraft to compensate for anywing heaviness due to'causes other than unbalanced fuel loading. Whensuch an adjustment has been made, cam member --66 may be secured to thecontrol linkage in its neutral position as shown in the drawingwhereupon subsequent operation of the trib tab control linkage upon theoccurrence of an unbalanced fuel loading will cause switch arm 52 to .berotated into its proper operative position. It should also be noted thatshould the means for transferring fuel from either of the tanks 10 or 11become inoperative, the fuel from such tank may be transferred to theopposite tank and subsequently transferred to the engines of theaircraft. In this manner, all the fuel in the fuel tanks may be utilizedeven though the normal means for transferring the fuel from one of thetanks should become inoperative.

It is apparent from the foregoing that there is provided a new and novelaircraft fuel load equalizing system which senses unequal fuel loads inwing tip or outer Wing fuel tanks and wherein the optimum balancingspeed may be obtained. All the fuel carried in either of the fuel tanksof the aircraft may be used even though the means fortransferring fuelfrom one of the tanks should become inoperative during operation, andthe system is simple and inexpensive in construction.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

I claim:

1. In an aircraft having a plurality of fuel tanks disposed on oppositesides of the longitudinal axis thereof, a fuel load equalizing systemwhich comprises fuel feed conduits connected to said tanks, an auxiliaryconduit connected to each of said fuel tanks and providing communicationtherebetween, pump means connected in said auxiliary conduit forcontrolling the flow of fuel therethrough, aileron members mounted inthe wings of said aircraft, trim tab control surfaces pivotally mountedon said aileron members, means forming part of the control linkage ofsaid aircraft and controlled by the pilot thereof for operating saidaileron members, means also 5 forming part of the control linkage ofsaid aircraft for operating said trim tab control surfaces independentlyof said aileron members, and means operative upon a predeterminedmovement of said trim tab control surfaces for controlling the operationof said pump means.

2. In an aircraft having a plurality of fuel tanks disposed on oppositesides of the longitudinal axis thereof, a fuel load equalizing systemwhich comprises fuel feed conduits connected to said tanks, an auxiliaryconduit connected to each of said fuel tanks and providing communicationtherebetween, reversible pump means connected in said auxiliary conduitfor controlling the flow of fuel therethrough, aileron members mountedin the wings of said aircraft, trim tab control surfaces pivotallymounted on said aileron members, means forming part of the controllinkage of said aircraft and controlled by the pilot thereof foroperating said aileron members, means also forming part of the controllinkage of said aircraft for operating said trim tab control surf-acesinde- 6 pendently of said aileron members, a circuit for energizing saidpump means, said circuit including a cam-actuated switch, and a camconnected to said trim tab operating means for actuating said switch toenergize said pump means upon a predetermined movement of said trim taboperating means.

3. A system as defined in claim 2 wherein said pump means includes anelectric motor connected in said circuit and adapted to be driven inopposite directions dependent on the direction of electric current flowtherethrough.

References Cited in the file of this patent UNITED STATES PATENTS2,356,786 Harman et a1 Aug. 29, 1944 2,672,880 Hermanson Mar. 23, 19542,755,046 Underwood July 17, 1956

